The present disclosure relates to the subject matter disclosed in German applications No. 101 24 483.5 of May 19, 2001 and No. 200 09 335.5 of May 24, 2000, which are incorporated herein by reference in its entirety and for all purposes.
The invention relates to a position or path measuring system comprising a transmitter and a sensor which comprises at least one inductive element, to which the transmitter is coupled electromagnetically, wherein sensor and transmitter can be positioned relative to one another and the at least one inductive element is arranged on a support so as to be areally extended.
Position measuring systems of this type are used, for example, for measuring positions on pneumatic cylinders, for measuring the position of valves, in particular, in closed-loop control circuits or in gripping devices. It is very advantageous for such uses when a relative path between transmitter and sensor can be measured absolutely.
It is known from DE 42 05 957 A1 to provide a transmitter guide which is movable relative to a coil structure with a triangular attenuating surface consisting of an electrically conductive material, wherein the attenuation increases, the nearer the coil structure approaches the end of the attenuating surface which reaches over the entire width of the transmitter guide.
The object underlying the invention is to improve a position measuring system of the type specified at the outset in such a manner that a great number of possibilities for its use result.
This object is accomplished in accordance with the invention in that the support with the at least one inductive element is designed to be at least partially flexible.
The shape of the support may be varied due to its flexible design and, in particular, varied such that the support with the inductive element arranged thereon can be curved, i.e. can be brought into a shape which is not flat. For example, the support may, as a result, be adapted to contours of an object in order to be able to carry out a position determination in the case of curved path movements. If, for example, the support is adapted to the path curvature, the relative distance between the support and the transmitter may be kept constant even with a curved path movement and so the position determination is not influenced by any alteration in the relative distance, i.e. the sensor signal experiences in accordance with the invention a change solely due to the movement along the path direction and not along transversely to the path direction.
As a result of an at least partially flexible design of the support, the useful length range with respect to the position determination of the position measuring system is also increased, namely with the same length of a corresponding measurement section or with the same useful area the length of the corresponding measurement section is reduced: Edge areas of the inductive element influence the sensor signal so that a non-monotonic dependence of a characteristic value of the inductive element, such as factor Q or effective inductance, results, for example, at these areas. This means for the application that only a certain section of the inductive element can be used for the position determination and the edge areas outside this are necessary in order to provide the areally extended inductive element but, otherwise, increase the length of the system. In the case of a flexible design of the support, such edge areas can be bent away and, in particular, folded out of the measurement field so that the length of the measurement section can be reduced along the measurement direction. As a result, an increase in thickness is caused to a certain degree but this may be kept slight in that, for example, the edge sections bent away are folded or rolled behind the support.
It is advantageous when the at least one inductive element is imprinted on the support. As a result, an areal extension thereof may be provided in a simple manner and corresponding path conductors may also be produced so as to be thin so that a flexibility of the support is ensured at least in a section with the inductive element arranged thereon.
A flexible design of the support may be achieved in a simple manner when this comprises a flexible foil. The flexible foil is a printed circuit board foil, on which the inductive element is arranged. A foil has a bending flexibility parallel to its surface in its normal directions.
It is particularly advantageous when the support comprises a rigid support section and one or more flexible support sections which are arranged on the rigid support section. The flexible support sections may then be bent away from the rigid support section in order to move them out of the measurement field of the sensor. The length of the usable measurement range is then determined by the dimensions of the rigid support section.
It is advantageous when, for providing a usable measurement area with respect to the at least one inductive element, one or more edge sections of the support are arranged with respect to the measurement section of the support in such a manner that they are located outside a measurement field. The length dimensions of the measurement section in a position measuring direction determine the usable distance measuring area and also the outer dimensions of the sensor since the edge sections may be bent away from the measurement section and, therefore, contribute nothing or only little to the longitudinal extension of the sensor. The measurable path is then essentially determined by the length of the measurement section.
Due to the edge section or sections of the support, end edge areas of the at least one inductive element are favorably located outside the measurement field. Such end edge areas, such as, for example, the apexes of triangles in the case of a triangular flat coil as inductive element, influence the sensor signal since, on the one hand, a transition takes place at this point between an electromagnetically couplable area and an area which is not electromagnetically couplable and since, on the other hand, the winding density and also line directions, for example, differ more greatly at these edge areas than in the case of areas outside these edge areas.
It is favorable when the measurement section of the support is of a rigid design since the edge sections of the support may then be folded away in a simple manner and may also be positioned behind the measurement section in order to keep the thickness extension slight as a result of the edge sections being bent away.
The edge section or sections of the support are advantageously arranged so as to be flexible with respect to the measurement section in order to be able to bend them away from it. This may be achieved, for example, in that a flexible foil is arranged on a rigid subsupport which has essentially the dimensions of the measurement section. This flexible foil is then connected to the measurement section so that the support is rigid in this area. Outside the subsupport the measurement foil may be bent relative to it and therefore to the measurement section. An alternative possibility is to arrange the edge sections themselves on the measurement section so as to be flexible, for example, to arrange them on a rigid printed circuit board so as to be flexible.
It is, furthermore, favorable when an edge section is arranged on the measurement section so as to be bent away or to be bendable away from it in order to limit the usable measurement area essentially to the measurement section.
In order to keep the thickness dimensions transversely to the measurement direction small, the edge section or sections are favorably positioned behind the support in relation to a measurement field. On the one hand, they do not interfere with the measurement and, on the other hand, the corresponding thickness dimensions of the sensor are kept small. For this purpose, an edge section is, in particular, arranged so as to be rolled and, in particular, rolled behind the support or an edge section is arranged so as to be folded and, in particular, folded around behind the support.
In a variation of one embodiment which is simple to produce from a technical point of view, the at least one inductive element is a printed coil which is imprinted on the support.
For the simple evaluation of a sensor signal, the at least one inductive element is favorably coupled to an oscillator and influences this via a factor Q and/or an effective inductance. The factor Q and/or effective inductance of the inductive element is advantageously determined by the size of an effective sensor area which is coupled to the transmitter and the sensor is designed such that the size of the effective sensor area is dependent on the relative position between transmitter and sensor transversely to a path direction. As a result of the fact that the inductive element is coupled to an oscillator and influences characteristic values of the oscillator, such as amplitude, phase position and frequency, via its factor Q and/or its effective inductance, a coupling of a transmitter to the inductive element, which is dependent on location, may be evaluated in a simple manner in that the corresponding characteristic values of the oscillator are evaluated. The inductive element is coupled to the oscillator such that this can be influenced itself. A special case of the coupling of the inductive element to the oscillator is the fact that the inductive element itself forms the inductance of the oscillator. Therefore, no primary coil need be supplied with energy and so a simple construction of the position measuring system can be achieved. The transmitter may be designed as a passive element and so it need not be acted upon with current via energy supply lines.
The sensor signal is determined by the geometric structure of the sensor or the transmitter, respectively. The information concerning the relative position between transmitter and sensor and, therefore, the distance information, path information or position information of the relative position between transmitter and sensor is contained in the geometric shape of the effective sensor area. The effective sensor area is, again, determined by the shape given to the sensor and, therefore, in particular, by the shape given to the inductive element. The inventive position measuring system may be designed in a simple manner and produced inexpensively as a result.
The position measuring system may be used universally and, in particular, in a rotary transmitter, as well, due to a corresponding design of the sensor. Apart from the inductive element, no further secondary coil or the like need be provided. In principle, it is sufficient to use a single, inductive element which is designed such that an effective sensor area is dependent on the relative position between transmitter and sensor. In addition, it is, however, also possible to provide additional, inductive elements. In this way, difference measurements or cumulative measurements may, for example, be carried out in order to obtain a high measurement accuracy or measurement resolution. For example, it may be provided in accordance with the invention for several measurement tracks to be used, for example, a measurement track for rough measurements and a measurement track for fine measurements. Since the information concerning location is in fact contained in the shape given to the effective sensor area, a great number of possibilities for use may be realized by adapting the shape.
A resolution for the measurement may be adjusted directly via the shape given to the effective sensor area. In this respect, resolutions at least in the order of magnitude of one thousandth of the total distance, which sensor and transmitter can take up relative to one another, can be realized without any problem.
Since the sensor signal is determined by an effective sensor area and, therefore, the sensor signal is determined directly by an effective inductance of the inductive element of the sensor, known evaluation circuits for inductive proximity switches, with which the approach of a metal object towards an oscillator coil is registered, for example, via a change in the amplitude or a change in the frequency of the oscillator, can be used. It is therefore possible to use evaluation units which are already available. The inventive position measuring system may be provided, in particular, with a type of evaluation unit irrespective of the special configuration of the transmitter or the inductive element since the evaluation unit essentially determines only a characteristic value of this inductive element.
The sensor is preferably designed such that an area of overlap between a projection of an effective transmitter surface area onto the sensor and an effective sensor surface area is dependent on the relative position between sensor and transmitter transversely to a direction of projection. The relative position between sensor and transmitter transversely to the direction of projection (transversely to the distance direction between sensor and transmitter) may be determined from this dependency.
An evaluation unit is provided, in particular, and this determines a characteristic value of the oscillator. A transmitter which is of a metallic design and, in particular, is electrically conductive, represents a counterinductance to the inductive element of the sensor. The coupling of the inductance causes a change in the effective inductance of the inductive element on the flexible support. This change in the effective inductance may be measured in a simple manner. In a variation of one embodiment it is provided for a frequency of the oscillator, to which the inductive element is coupled, to be measured as characteristic value. The frequency of an LC oscillatory circuit is essentially inversely proportional to the root of the effective inductance. This may be determined in a simple manner. This variation is particularly advantageous when the transmitter is a magnet and, in particular, a permanent magnet since, as a result, a relatively large change in inductance can occur which affects the frequency of the oscillatory circuit accordingly, in particular, when a soft magnetic material, which can be brought into a state of saturation locally, is arranged on the sensor.
In an alternative variation, an amplitude of the oscillator, to which the at least one inductive element is coupled, is determined. The amplitude of an oscillator and, in particular, an oscillatory circuit is, again, dependent on the effective inductance or factor Q of the inductive element of the sensor. It may be determined in a simple manner. It is possible to determine changes in amplitude which are relatively small. The effective inductance may also be evaluated when the transmitter is a non-magnetic metal.
It may be provided for the evaluation unit to be arranged on a support, on which the at least one inductive element is seated. Evaluation unit and inductive element are then integrated on one support, wherein provision must be made, however, for the flexibility of the support at least in one section. The sensor may be produced in a simple and inexpensive manner as a result of this integrated arrangement and the installation, for example, in a housing is accordingly simple during use.
The measurable path is favorably determined by the length of a measurement section, on which the at least one inductive element is arranged such that end edge areas of the inductive element are located outside the measurement section. As a result, edge effects with respect to effective sensor surface areas may be eliminated to a certain extent since the edge areas of the inductive element causing the edge effects are moved out of the measurement field.
It is particularly advantageous when the transmitter is a passive element and is, in particular, produced from an electrically conductive or magnetically conductive material. A passive transmitter is a transmitter which is not connected to a source of energy and nevertheless causes an electromagnetic coupling to the inductive element. In particular, no energy supply lines for the transmitter, which would perhaps have to be moved with it, need be provided.
In a particularly simple variation of one embodiment, which can also be produced inexpensively as a result, the transmitter comprises a magnet and, in particular, a permanent magnet. Its magnetic field influences the inductive element and this influence is again expressed in a change in the effective inductance. This change is, again, dependent on the effective sensor area of the inductive element which is acted upon by the magnetic field. With such a transmitter it is also possible to measure through metallic walls. For example, the position of a piston provided with such a transmitter may be detected from the outside through a wall of a pressurized cylinder consisting of aluminum.
In this respect, it is favorable when soft magnetic material is arranged on or in the vicinity of the inductive element. In the case of the soft magnetic material, this is, for example, a Mu metal in the form of a foil which has as high a permeability as possible and as small an electric conductivity value as possible. As a result of the magnetic field of the transmitter, the soft magnetic material may be brought locally into a state of saturation; an effective sensor area is defined by this local saturation. The local saturation at the effective sensor area again causes a relatively strong change in the effective inductance which can therefore be easily detected.
For example, the soft magnetic material is, for this purpose, applied to the support on one side or on both sides. It may also be provided for the soft magnetic material to be wound around the support.
In principle, an effective sensor area, which is dependent on the positioning of a transmitter in relation to the sensor, can be adjusted in that the at least one inductive element is designed in such a manner that its shape along a measurement path varies transversely to the measurement path. It is also possible, alternatively or in addition, for the soft magnetic material to be arranged in such a shape that the shape dimension in relation to a measurement path varies along the measurement path. Since an effective sensor area can be brought into a state of saturation locally due to the soft magnetic material, an effective sensor area is also determined by the design of the soft magnetic material itself. Outside the soft magnetic material, the magnetic field action of the sensor is different to that at the soft magnetic material, and the effective sensor area is therefore determined by the type of application of the soft magnetic material. It is provided, in particular, for the soft magnetic material to be arranged in the form of a triangle. As a result, the transverse dimensioning of the soft magnetic material varies along the measurement path and the relative position between transmitter and sensor may be determined via the variation in the transverse dimensioning.
It is favorable when the at least one inductive element is designed in such a manner that its shape transverse to a measurement path varies along the measurement path. This may be achieved in a simple manner via the corresponding design of the windings of a flat coil. The effective sensor area varies due to the alteration in its shape transversely to the measurement path. The size of the effective sensor area is again responsible for the sensor signal and this sensor signal then contains the information concerning the relative position.
It is particularly favorable when a magnetic screening is provided for the at least one inductive element in the form of a xe2x80x9cmagnetic cagexe2x80x9d so that interference fields, such as the earth""s magnetic field, do not influence the position determination. The magnetic screening screens not only the inductive element but also the transmitter.
In the case of the inventive distance measuring system it is possible to design the sensor such that via the corresponding shaping a specific characteristic curve of the position measuring system for a sensor signal can be and, in particular, is adjusted as a function of a measurement path. For example, an at least approximately linear signal curve can be set in order to be able to allocate a measurement parameter in a simple manner to a specific distance measuring path.
In order to monitor the functioning of the position measuring system it is advantageous when an error signal can be derived from the evaluation unit, wherein it can be checked whether one or more parameters of the inductive element are in a tolerance range. It is checked, in particular, whether the factor Q and/or effective inductance do not deviate to too great an extent upwards or downwards from still acceptable values. A plausibility check may then be carried out, with which a break in the coil, a short circuit or even a failure/movement of the transmitter out of the measurement area may, for example, be detected.
In a variation of one embodiment which is simple to produce, the at least one inductive element is of a triangular design and, in particular, it has triangular windings. If the direction parallel to a vertical direction of the triangle is selected as measurement direction, the transverse extension of the triangle then decreases or increases linearly in one direction so that a varying effective sensor area may be adjusted geometrically in this way.
The following description of preferred embodiments serves to explain the invention in greater detail in conjunction with the drawings.